Method for Assaying the Lipid Kinase Phosphatidylinositol-5-phosphate 4-kinase α in Quantitative High-Throughput Screening (qHTS) Bioluminescent Format

PI5P4K inhibitors: promising opportunities and challenges

Phosphatidylinositol 5-phosphate 4-kinases (PI5P4K), also known as type II PIPKs or PIPKIIs, convert the lipid second messenger PI5P to PI(4,5)P2. The PI5P4K family consists of three isozymes in mammals-PI5P4Kα, β, and γ-which notably utilize both GTP and ATP as phosphodonors. Unlike the other two isozymes, which can utilize both ATP and GTP, PI5P4Kβ exhibits a marked preference for GTP over ATP, acting as an intracellular GTP sensor that alters its kinase activity in response to physiological changes in GTP concentration. Knockout studies have demonstrated a critical role for PI5P4Kα and β in tumorigenesis, while PI5P4Kγ has been implicated in regulating immune and neural systems. Pharmacological targeting of PI5P4K holds promise for the development of new therapeutic approaches against cancer, immune dysfunction, and neurodegenerative diseases. Although several PI5P4K inhibitors have already been developed, challenges remain in PI5P4K inhibitor development, including a discrepancy between in vitro and cellular efficacy. This discrepancy is attributable to mainly three factors. (a) Most PI5P4K inhibitors were developed at low ATP levels, where these enzymes exhibit minimal activity. (b) Non-catalytic functions of PI5P4K require careful interpretation of PI5P4K depletion studies, as their scaffolding roles suppress class I PI3K signaling. (c) The lack of pharmacodynamic markers for in vivo assessment complicates efficacy assessment. To address these issues and promote the development of effective and targeted therapeutic strategies, this review provides an analytical overview of the distinct roles of individual isozymes and recent developments in PI5P4K inhibitors, emphasizing structural insights and the importance of pharmacodynamic marker identification.

Multimodal action of KRP203 on phosphoinositide kinases in vitro and in cells

Increased phosphoinositide signaling is commonly associated with cancers. While "one-drug one-target" has been a major drug discovery strategy for cancer therapy, a "one-drug multi-targets" approach for phosphoinositide enzymes has the potential to offer a new therapeutic approach. In this study, we sought a new way to target phosphoinositides metabolism. Using a high-throughput phosphatidylinositol 5-phosphate 4-kinase-alpha (PI5P4Kα) assay, we have identified that the immunosuppressor KRP203/Mocravimod induces a significant perturbation in phosphoinositide metabolism in U87MG glioblastoma cells. Despite high sequence similarity of PI5P4K and PI4K isozymes, in vitro kinase assays showed that KRP203 activates some (e.g., PI5P4Kα, PI4KIIβ) while inhibiting other phosphoinositide kinases (e.g., PI5P4Kβ, γ, PI4KIIα, class I PI3K-p110α, δ, γ). Furthermore, KRP203 enhances PI3P5K/PIKFYVE's substrate selectivity for phosphatidylinositol (PI) while preserving its selectivity for PI(3)P. At cellular levels, 3 h of KRP203 treatment induces a prominent increase of PI(3)P and moderate increase of PI(5)P, PI(3,5)P2, and PI(3,4,5)P3 levels in U87MG cells. Collectively, the finding of multimodal activity of KRP203 towards multi-phosphoinositide kinases may open a novel basis to modulate cellular processes, potentially leading to more effective treatments for diseases associated with phosphoinositide signaling pathways.

Inexpensive High-Throughput Screening of Kinase Inhibitors Using One-Step Enzyme-Coupled Fluorescence Assay for ADP Detection

Protein kinases are attractive targets for both biological research and drug development. Several assay kits, especially for the detection of adenosine diphosphate (ADP), which is universally produced by kinases, are commercially available for high-throughput screening (HTS) of kinase inhibitors, but their cost is quite high for large-scale screening. Here, we report a new enzyme-coupled fluorescence assay for ADP detection, which uses just 10 inexpensive, commercially available components. The assay protocol is very simple, requiring only the mixing of test solutions with ADP detection solution and reading the fluorescence intensity of resorufin produced by coupling reaction. To validate the assay, we focused on CDC2-like kinase 1 (CLK1), a dual-specificity kinase that plays an important role in alternative splicing, and we used the optimized assay to screen an in-house chemical library of about 215,000 compounds for CLK1 inhibitors. We identified and validated 12 potent inhibitors of CLK1, including a novel inhibitory scaffold. The results demonstrate that this assay platform is not only simple and cost-effective, but also sufficiently robust, showing good reproducibility and giving similar results to those obtained with the widely used ADP-Glo bioluminescent assay.